The invention relates to a high-temperature sensor with a metallic protective tube and a measuring resistance which is surrounded by a ceramic powder.
Metallic protective tube denotes a metallic casing enclosing the temperature sensor's components, whereby a part of the protective tube enclosing the measurement element protrudes into the medium and an outer part of the protective tube holds the connecting cables leading outside.
Process adapter means the mechanical interface, e.g. a pipeline, between the temperature sensor and the recipient containing the medium whose temperature shall be acquired.
The electrical adapter is the interface between the inner cables running inside the casing and the outer connecting cables.
The preferred field of application is in temperature measuring points with heavy mechanical and thermal duty, e.g. in exhaust ducts of combustion engines.
In order to improve the engine management system of combustion and gas engines temperature sensors are needed, whose working temperature is in the range from 600° C. to 900° C. The measuring points for the temperature sensors are mostly in a part of the exhaust duct close to the engine. The chemical-corrosive, mechanical and thermal operational conditions present when measuring exhaust gas temperatures make very high demands on the temperature sensor's components and require elaborate means regarding the materials to be employed and sophisticated measures for holding the components steady and designing the components connections.
A multitude of arrangements for solving particular problems out of the aforementioned ones is known as prior art.
For instance, DE 199 34 738 A1 and DE 100 62 041 A1 are known, which claim to achieve an improved technology in design and connections between the sensor and the inner cables by encapsulating the temperature sensor's connection-sided part with a temperature-proof, electrically non-conductive material or by forming it with an overlapping connection of the thermistor contacts and the inner signal cables and a tight fit.
Technical measures for saving the measuring element are given in DE 30 12 787 A1 and DE 199 22928 A1.
Different measures regarding protection against sensor harming ambiences are given in DE 298 23 459 U1 and EP 0774 650 A1.
EP 0774 650 A1 suggests to arrange a mechanically stable and liquid-tight connection in the connective area of a tube-shaped casing for allowing the influx of atmospheric oxygen from the environment via a connective cable into the casing. Furthermore it is known from DE 298 23 459 U1 to permit the oxygen influx via a special neck pipe opening. However besides the complicated design the necessity to apply openings to the sensor mounts is a disadvantage.
Solutions for improving metrological heat dissipation and radiation errors are given in DE 199 39 493 A1 and DE 298 23 379 U1.
Arrangements for improving the protection of the mechanical armature components, which achieve an adaption to specifications for strength and production by different diameter geometry are given in DE 100 34 265 A1 and DE 199 41 188 A1.
Disadvantages in the described arrangements besides the elaborate and expensive production are that in each case only particular ones out of the aformentioned problems are faced, thus the causes for metrological, electrical or mechanical malfunctions are not eliminated generally.
Furthermore for thermocouples arranged inside ceramic protective tubes it is known from DE 42 07 317 C2, DE 16 48 261 A and U.S. Pat. No. 5,209,571 A to use powders inside the protective tubes which oxygen-reducing components are added to in order to protect the thermo wires applied in these arrangements against oxidation and thus extend their life cycle. However these measures are not applicable for arrangements with platinum resistive sensors because reductive conditions would reduce the life cycle of the platinum resistor.
It is the object of the invention to specify a high temperature sensor of the aforementioned kind which can be applied at a temperature of at least 600° C., which resists to high mechanical and chemical stress, which can be made technologically convenient and which improves reliability and life cycle compared to known temperature sensors.